Exactly why the immune system begins to produce these aberrant antibodies is unclear. Heredity and other characteristics seem to play a role in determining susceptibility. Studies show, for example, that if one identical twin contracts Graves' disease, there is a 20% likelihood that the other twin will get it, too. Also, women are more likely than men to develop the disease. And smokers who develop Graves' disease are more prone to eye problems than nonsmokers with the disease. No single gene causes Graves’ disease. It is thought to be triggered by both genetics and environmental factors.